Google has tightened integration between Google Base and Google Checkout. Google now allows Base users to specify Google Checkout as the payment option on bulk uploads. Some observers, such as ZDNET's David Berlind, have noted that Google Checkout means Google is just baby steps away from launching an eBay-like service.
The combination of Google Base and Google Checkout effectively creates such a service. But, that combo has neither the personality nor the marketing to compete with the auction giant. And personally, I don't think GBase was ever intended to be anything other than a proof-of-concept for Google. It's a product that allows Google to benefit by doing trend analysis on the few hundred thousand items that users upload.
If Google's thinking online auctions, it's probably thinking much bigger than eBay. How big? So big it won't have a single site associated with it. Google will empower every user to integrate Checkout into his or her own site (preferably created using Google Base or Google Page Creator). And, it'll also make buying and selling easy by integrating Checkout with everything you upload (should you choose to exercise this option) to GDrive.
In effect, Google is probably working towards an Edgeio-like solution to online marketplaces. The difference is that Google has a foot in the door, since it already has its apps on your desktop.